The page on Kuriyama Mirai on Kyoukai no Kanata Wiki says she uses her ring to activate her ability.
From the show, I got the feeling the ring was something that kept some of her powers on check, rather than an activator.
I don't recall any explanation of how the ring works during the series.
Whichever the case may be, how exactly does the ring help her control/activate her ability?
Does the ring possess some kind of magic? Or is it some kind of psychological power it exerts over Mirai?